From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Thu, 24 Mar 2011 10:33:30 +0100
Thread-Topic: VLF: Resonate the antenna, or not?
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Subject: RE: VLF: Resonate the antenna, or not?
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Hello Piotr, Stefan, Scott,

based on 6.5mm wire diameter and a skin depth of 0.925mm I come to an effe=
ctive area of 16.2mm and thus a resistance of 0.174 Ohm for 100m wire (bas=
ed on a resistivity for Al =3D 2.82E-8 Ohm*m, see http://en.wikipedia.org/=
wiki/Electrical_resistivity_and_conductivity#Resistivity_of_various_materi=
als)
What is the same as Piotr's result.
Using IN3OTD's formula I come to a loop inductance of 161 uOhm what also=
 agrees well with Poitr's calculation.
The ERP values calulated by Poirt seem also correct to me.

The maximum current for a 6.5mm (2 AWG) Al wire is 100A DC (see http://www=
.engineeringtoolbox.com/maximum-current-copper-aluminum-wire-d_1690.html).=
 At 9kHz the current runs only trough about 50% of the wire area (skin eff=
ect), so 100A might be too much.

73, Rik  ON7YD - OR7T
________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or=
g] namens Piotr Mlynarski [sq7mpj@toya.net.pl]
Verzonden: donderdag 24 maart 2011 3:27
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: VLF: Resonate the antenna, or not?

Stefan Sch=E4fer pisze:
> Wow, nice!
>
> Rik/ON7YD, now its your turn again: What will be the ERP when running
> 100A in that wire? I think 100A is realistic on such a wire. Skin
> depth should be 0.9 mm. So the effective conductor area 19 mm^2.
> Assuming 20m x 30m (?) wire (=3D600m^2) means 100m length, so R ~ 0.15
> Ohm. So Scott gets 100 A rms when running 1.5 kW into the antenna (no
> problem for the mains), without having problems of winding a large
> coil, without resonating, without ferrite parts, without high voltages
> (but high currents ;-) ). Am i right, Rik? And what is the ERP? I
> could take a look on your website but you can do it so well here! What
> is the L and Z and so the needed voltage to get 100A? :-)
> Instead of standard FETs, some IGBTs could be used, shouldn't be a
> problem at 9 kHz and some 100V. Any recommendations? :-)
>
> Scott, what FETs do you use in your design? The IRFP460 is OK for 20 A
> but not much more. One could do the effort and switch 4x 10 of them in
> parallel but you'll need a good driver, maybe IXDD430... Interesting
> stuff!
>
> 73, Stefan EI/DK7FC

Hi Stefan,  LF group

 Just before i was  going to switch off my computers and go to bed
your mails arrived ....
 below my quick calculations   / Rik , pse, check it out :)  /
Al wire diameter 6.5 mm length 100 meters, f=3D 8970 Hz
skin depth: 0.925 mm   so Rac @ 8970 Hz  =3D 0.174 Ohm
20m x 30 m rectangular loop - its inductance L =3D 162.85 microHenry
/RA9MB equation/
radiation resistance Rrad =3D 0.008994 microOhm  / or using picoOhms as in
recent examples 8994 pOhm/
2*pi*f*L =3D 9.178 Ohm
2*pi*f*L/Rac =3D 52.72

using enough pwr to develop 100 Amp current  TX radiated is 89.94 microwat=
ts
loop over ground i.e. twice the Rad along with -0.39dBd loop gain
results in ERP =3D 164.4 microWatts
Voltage loop around 918 Volt

                                                           73, Piotr, sq7m=
pj

qth: Lodz /jo91rs/